This invention relates to phosphor pastes used in the manufacture of plasma display panels (PDP). More particularly, this invention relates to the brightness maintenance of phosphor pastes after binder burn-out.
There exists tremendous market potential for plasma display panels for both home entertainment and computer applications. In order to succeed in these markets, plasma display panels must meet or exceed the performance of standard cathode ray tubes (CRT). As with cathode ray tubes, the performance of the plasma display panels center on the performance of the phosphors which make up the displays and their methods of application.
In the manufacture of PDP panels, the phosphors are applied to an inner panel surface by screen-printing patterns of pastes containing red, green, and/or blue-emitting phosphors. Typical PDP phosphors include the red-emitting (Y,Gd)BO3:Eu phosphor, the blue-emitting BaMgAl14O23:Eu2+ phosphor, and the green-emitting Zn2SiO4:Mn phosphor. Paste characteristics such as viscosity, print thickness, thixotropy, surface tension, and binder burn-out have an effect on the screen-printing ability of the phosphor-containing pastes and the overall quality of the plasma display panel. In addition the phosphor, PDP paste compositions typically include a binder, an organic solvent, dispersants and plasticizers. The phosphor generally comprises from about 35 to about 65 percent by weight of the paste. Prior art binders include ethyl cellulose and polymethyl methacrylate. The amount of the binder in a paste may vary from about 0.5 to about 10% by weight. The dispersant is important for the paste stability, i.e., maintaining a homogeneous suspension of phosphor particles in the paste for long duration of time without separation of the solids. Typical viscosity requirements for PDP pastes range from about 30,000 to 60,000 centipoise.
Pastes should be formulated to minimize any negative effects on phosphor brightness during panel manufacturing. In particular, the organic components of the pastes are burned-out during panel manufacturing by heating the panels to about 500xc2x0 C. in an oxygen-containing atmosphere for about 1-2 hours. This burn-out step can severely impact the brightness of the PDP phosphors. Particularly, those phosphors which contain activator ions susceptible to oxidation, e.g., BaMgAl14O23:Eu2+. A typical brightness loss for this blue-emitting PDP phosphor can be greater than 20% following burn-out.
It is an object of the present invention to minimize the decrease in the brightness of PDP phosphors resulting from the burn-out of the organic paste components.
It is another object of the invention to provide pastes which are capable of being used in the screen-printing of plasma display panels.
It is yet another object of the invention to provide pastes of blue, red and green PDP phosphors with improved paste stability.
In accordance with an object of the invention, there is provided a phosphor paste for plasma display panels comprising a phosphor dispersed in an organic paste comprising a solvent, a binder, at least one dispersant comprising stearic acid, and a plasticizer.
In accordance with another object of the invention, there is provided a phosphor paste for plasma display panels comprising a phosphor dispersed in an organic paste containing a binder and stearic acid, said phosphor retaining at least about 90% of its initial brightness after said binder has been burned-out.